Influences of hydrodynamic shear force on selectin-mediated neutrophil rolling dynamics in vitro

The cellular immune response to infection and tissue injury requires the recruitment of leukocytes in blood. This process is mediated by a well-known multistep cascade, which involves transient tethering, subsequent rolling on the endothelium and recognition of inflammation followed by extravasation. The underlying aim of this work is to investigate the effects of hydrodynamic force on adhesion molecules on neutrophil surface and their consequences on the recruitment of neutrophils to an inflamed site. A crucial finding obtained with flow chamber experiments using isolated human neutrophils in vitro, is that L-selectin constitutively expressed on the surface of neutrophils can be shed mechanically during rolling under shear flow without exogenous stimuli. This mechanical shedding of L-selectin depends on the shear force applied and was mathematically modeled by adhesive dynamic simulation with the Bell model of dissociation to describe L-selectin shedding. In addition it has been shown, using immunoflourescent microscopy of L-selectin on neutrophils in vitro, that L-selectin can be localized by the shear force introduced by centrifugation. The shear-induced redistribution of L-selectin was also examined using a theoretical model of a viscous drop in flow. This study suggested an alternative explanation of the localization of L-selectin on the surface of neutrophils recruited on an E-selectin-surface under flow. Furthermore, I have found that microcontact printing of P-selectin increases the rate of neutrophil recruitment in flow chamber experiments, suggesting that it is important to have the proper orientation of adhesion molecules on a substrate for capturing leukocytes. Finally, we have explored, using a microfabricated biocompatible structure and covalently attached P-selectin, respectively, that the potential applications of capturing target cells mediated by the receptor-ligand binding under flow. Overall, the hydrodynamic environment of blood plays an important role in regulating the recruitment of leukocytes by affecting the expression and distribution of adhesion molecules.